(1) Field of the Invention
The present invention relates to partial pressure measuring methods and partial pressure measuring apparatuses, and more particularly to a partial pressure measuring method and a partial pressure measuring apparatus for measuring partial pressure in a vacuum chamber.
(2) Description of the Related Art
For mass production process of various products such as electronic components and optical thin films, surface modification for introducing a small amount of gas into a vacuum chamber thereby causing reaction on a substrate surface; dry etching for processing a surface by generating plasma; sputtering for forming a film; Chemical Vapor Deposition (CVD); and the like have been widely used.
In order to perform homogeneous processing on the substrate surface, it is desirable that concentration of the small amount of gas is homogeneous in the vacuum chamber. Therefore, it is vital to know concentration distribution of the small amount of gas in the vacuum chamber and also control the concentration of the small amount of gas.
One example of such processing is sputtering by which a film is formed on a substrate by generating plasma in a vacuum. Reactive sputtering is one of methods for forming oxide or nitride as a film at a high speed using sputtering. By the reactive sputtering, a DC voltage is applied to a metal target in a vacuum chamber to generate plasma. Thereby, atoms sputtered from the metal target by the generated plasma are reacted with reactive gas introduced into the vacuum chamber. As a result, oxide or nitride is deposited on a substrate.
In order to obtain homogeneous composition of the compound thin film formed in the vacuum chamber, it is crucial to control distribution of the introduced gas to achieve homogeneous reaction. Therefore, gas partial pressure distribution in an apparatus which actually forms the compound thin film should be monitored and controlled. Here, regarding definition of the partial pressure, a pressure of certain gas among whole pressure of mix gas is called partial pressure of the certain gas. The partial pressure distribution means distribution of spatial partial pressure in a vacuum chamber.
One of conventional methods for measuring partial pressure distribution uses a mass analyzer, for example.
In the partial pressure distribution measuring method using a mass spectrometer, gas has to be brought to reach an analyzer tube of the mass analyzer. Therefore, when local partial pressure in a vacuum chamber is measured, it is necessary to set a pipe to reach a measuring location in the vacuum chamber. Furthermore, radius of the pipe should be short. However, if the radius of the pipe is shortened, conductance of the pipe is lowered, which fails to measure the partial pressure correctly. In addition, adsorption gas adhered to a surface of the pipe affects the measuring.
In order to address the above problem, it is known, from Japanese translation of PCT international application No. 02-25249, for example, to provide a method using a spectroscopic measuring apparatus, as a partial pressure measuring method without setting a pipe in a vacuum chamber.
In this technology, a spectroscopic analysis using a Laser Induced Fluorescene (LIF) is disclosed. The spectroscopic analysis using LIF can measure partial pressure at each location irradiated by laser.
FIG. 1 is a schematic block diagram of a conventional spectroscopic measuring apparatus. The spectroscopic measuring apparatus of FIG. 1 includes a vacuum chamber 1, a transparent window 2, a spectroscope 3, an optical fiber 4, a laser-oscillation power source 5, a laser unit 6, and laser-control optical unit 7.
In the spectroscopic measuring apparatus of FIG. 1, the transparent window 2 is formed on an external wall of the vacuum chamber 1, and laser 8 provided from outside by the laser unit 6 is irradiated to gas in the vacuum chamber 1. The irradiation of the laser 8 to the gas causes light emission when molecules of the gas are excited and back to the ground state. Partial pressure distribution at each location can be determined by measuring the intensity of the caused emission along a path of the laser 8.
However, the conventional spectroscopic measuring apparatus is generally quite expensive and requires a long time for the measuring since emission intensity is low. If the measuring is performed in a shorter time, noise is increased thereby reducing an accuracy of the measuring.
In addition, the conventional spectroscopic measuring apparatus has another problem. In the conventional spectroscopic measuring apparatus, every time of measuring each location in the vacuum chamber 1, optical systems such as the laser unit 6 and the spectroscope 3 need to be moved and adjusted. Therefore, mass production process is quite difficult to be introduced.
A number of solutions have been proposed to address the problem of the spectroscopic measuring apparatuses. Partial pressure measuring methods for reducing inconvenience of adjustment of optical systems and cost are disclosed in Japanese translation of PCT international application No. 02-25249, Japanese Unexamined Patent Application Publications Nos. 11-23666, 5-62944, and 58-46640, and Japanese translation of PCT international application No. 2005-276618, for example.
The Japanese Unexamined Patent Application Publication No. 11-23666 discloses a partial pressure measuring method of measuring partial pressure of H2O in a vacuum chamber by detecting plasma emission spectrum.
The Japanese Unexamined Patent Application Publication No. 05-62944 discloses a method of focusing plasma emission generated in a vacuum camber into a spectroscope, and then performing spectral analyzing of the plasma emission.
The Japanese Unexamined Patent Application Publication No 58-46640 discloses a method of performing spectral analysis on plasma emitted from a window formed on a vacuum chamber.
However, in the above-described technologies, the measuring is performed by using a part of plasma emission generated by a plasma source for process provided in the vacuum chamber (hereinafter, referred to as “process plasma source”). Therefore, intensity of such plasma emission generated by a process plasma source is relatively high, so that plasma emission regarding gas to be measured is not always measured accurately. In short, the above-described partial pressure measuring methods disclosed in these publications utilize plasma emission of a process plasma source provided in a vacuum chamber, thereby receiving not only plasma emission regarding gas to be measured but also plasma emission regarding gas not to be measured. As a result, the above-described partial pressure measuring methods have difficulty of achieving correct partial pressure measuring for target gas.
In the meanwhile, the Japanese translation of PCT international application No. 2005-276618 discloses that the process plasma source provided in a vacuum chamber is configured as a cylinder electrode. Such a process plasma source as a cylinder electrode restricts an angle and a position where plasma emission generated by the process plasma source can be received. Furthermore, the process plasma source disclosed in the Japanese translation of PCT international application No. 2005-276618 is movable, so that it is difficult to adjust the receiving and the measuring of plasma emission generated by the process plasma source. Therefore, this partial pressure measuring method also fails to perform correct partial pressure measurement for target gas in a vacuum chamber.